1. Field of the Disclosure
The present disclosure relates to an organic light emitting diode (OLED) display device and a method of driving the same, and more particularly, to an OLED display device and a method of driving the same, which may improve initialization characteristics to enhance response characteristics and solve luminance degradation.
2. Discussion of the Related Art
In recent years, as the information age has progressed, various needs for display fields have increased. To meet those needs, research has been conducted into various flat panel display (FPD) devices that are fabricated to be ultrathin and lightweight and consume low power, for example, liquid crystal display (LCD) devices, plasma display panel (PDP) devices, and organic light emitting diode (OLED) devices.
An OLED display device is an emissive display including organic compounds formed on a transparent substrate to emit red (R), green (G), and blue (B) light. In general, the OLED display device may include an OLED panel and a driver circuit.
Thus, the OLED display device does not require an additional light source unlike an LCD device.
As a result, since a backlight unit (BLU) is not required, the OLED display device may be fabricated using a simpler process at lower fabrication cost than the LCD device, and has attracted much attention as an advanced FPD.
Furthermore, the OLED display device may have a wider viewing angle and a higher contrast ratio than the LCD device, may be driven at a low direct-current (DC) voltage, have a high response speed, and be highly resistant to external shock and applicable within a wide temperature range.
In particular, in an active-matrix-type OLED (AMOLED) display device, a voltage for controlling current applied to a pixel region may be charged in a storage capacitor so that the voltage can be maintained until the next frame signal is applied. Thus, the AMOLED display device may be driven to maintain an emission state during display of one screen irrespective of the number of gate lines.
Accordingly, since the AMOLED display device exhibits the same luminance even with application of a low current, the AMOLED display device may reduce power consumption and be scaled up.
FIG. 1 is a schematic equivalent circuit diagram of a pixel region of a conventional OLED display device.
As shown in FIG. 1, in the conventional OLED display device, a gate line GL and a data line DL may be formed across each other to define a pixel region P, which may include a switching transistor Tsw, a driver transistor Tdr, a storage capacitor Cst, and an OLED.
The switching transistor Tsw may be connected to the gate line GL, the data line DL, and one end of the storage capacitor Cst.
In addition, the driver transistor Tdr may be connected to one end of the storage capacitor Cst, the OLED, and the other end of the storage capacitor Cst.
In this case, the OLED and the driver transistor Tdr may be connected between a high-potential voltage line VDD and a low-potential voltage line VSS.
The operation of the pixel region of the OLED display device will now be described. To begin with, when the switching transistor Tsw is turned on by supplying a gate signal through the gate line GL, a data signal applied through the data line DL may be transmitted to the driver transistor Tdr and the storage capacitor Cst.
Also, when the driver transistor Tdr is turned on in response to the data signal, current may flow through the OLED so that the OLED can emit light.
In this case, intensity of light emitted by the OLED may be proportional to the amount of current flowing through the OLED, which may be proportional to the magnitude of the data signal.
Accordingly, the OLED display device may apply a data signal having various magnitudes to the respective pixel regions P to produce various grayscales. As a result, the OLED display can display images.
Furthermore, the storage capacitor Cst may maintain the data signal during one frame so that the amount of current flowing through the OLED can be maintained constant, and a grayscale displayed by the OLED can be maintained constant.
Meanwhile, unlike a liquid crystal display (LCD) in which a transistor of a pixel region is turned on for only a relatively short time during one frame, in the OLED display device, the driver transistor Tdr may remain turned on for a relatively long time for which the OLED emits light to display a grayscale, so that the driver transistor Tdr can easily deteriorate.
As a result, a threshold voltage Vth of the driver transistor Tdr may vary. Variation in the threshold voltage Vth of the driver transistor Tdr may adversely affect the resolution of the OLED display device.
That is, the pixel region of the OLED display device may display different grayscales in response to the same data signal due to the variation in the threshold voltage Vth of the driver transistor Tdr, thereby exacerbating the resolution of the OLED display device.
Therefore, it is necessary to develop a new pixel structure of an OLED display device to compensate for a variation in threshold voltage caused by deterioration of a driver transistor.